1. Field of the Invention
The invention relates to a laser apparatus in which the lasing medium is a slab of rectangular cross section and to a laser apparatus in which the optical cavity is optimized for use with a rectangular slab.
2. Description of the Prior Art
Lasers employing a rectangular slab as the active medium conventionally are face pumped, with the pumping source being provided by a flash lamp having an appropriate spectrum, placed adjacent two lateral faces. In the conventional face pumped laser, the laser is installed in an optical cavity with the end faces of the slab providing the entrant surfaces for the laser beam. Conventionally, the laser slab is cut in a parallelogram or trapezoid configuration, as seen from the side, with the angles of the faces being cut at the Brewster angle for full acceptance of light of a "P" polarization with a minimum loss. The beam is introduced on the axis of the slab with the entrant beam being diffracted to the bottom lateral surface, reflected to an upper lateral surface and so forth until it emerges at the other end face, normally in an extension of the same line and coincident with it.
The output power of the face pumped slab laser is limited by the bulk of the laser slab and its heat dissipating properties. In the interest of increasing the output power, the bulk of the laser laser slab may be increased. However, if a square cross section is retained, heat dissipation performance worsens as the thickness of the material through which heat must pass is increased. On the other hand, a rectangular cross section in which the bulk of the slab is increased without increasing the thickness through which heat must pass, improves the heat dissipation performance. In principal, the width dimensions could be significantly increased and additional flash lamps and additional cooling applied to the major lateral faces of the slab to produce proportional increases in the output beam. Having selected a slab of rectangular cross section, one must provide efficient coupling between the optical resonator and the laser slab and at the same time maintain good output beam quality.